The present invention relates to a new and improved apparatus for sensing relative movement between a pair of members.
A Hall effect device and a pair of magnets have been used to detect relative movement between a pair of members. The Hall effect device has been connected with one of the members for movement therewith relative to the magnets which are connected with the other member. Upon relative movement between the two members, the Hall effect device cooperates with the magnets to create an electrical signal in a known manner.
Although the electrical signal provided by the interaction between the magnets and a Hall effect device has been widely used in many different environments to detect relative movement between a pair of members, difficulty has been encountered in accurately positioning the Hall effect device and magnets relative to each other in a neutral or initial position. If the Hall effect device and magnets are not initially positioned accurately relatively to each other, the Hall effect device will provide an output signal indicative of relative movement between the members when such movement has not occurred.
The concept of using a Hall effect device and a pair of magnets to detect initiation of a power steering operation is disclosed in U.S. Pat. No. 4,415,054. The power steering apparatus disclosed in this patent includes a steering column having an upper shaft which is rotated upon rotation of a steering wheel. Torque is transmitted from the upper shaft to a lower shaft by a torsion bar between the two shafts. The lower shaft is connected with the pinion of a rack and pinion steering gear.
Upon initiation of a steering operation with the apparatus disclosed in U.S. Pat. No. 4,415,054, the torsion bar is twisted and a Hall effect device mounted on the upper shaft is moved relative to the pair of magnets on the lower shaft. When the Hall effect device is moved relative to the magnets, a control signal is created which is delivered to an electronic control unit. The control signal indicates the amount of relative movement between the two shafts and the direction of this relative movement. If the magnets and Hall effect device of the apparatus disclosed in U.S. Pat. No. 4,415,054 are not initially positioned accurately relative to each other, an output signal indicating relative movement between the shafts is created prior to rotation of the steering wheel.